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Formula: Ca6(Si2O7)(SiO4)(OH)2
Sorosilicate (Si2O7 groups)
Crystal System: Triclinic
Specific gravity: 2.94
Streak: White
Colour: Colourless
Environments
Metamorphic environments
Hydrothermal environments
Localities
At the type locality, Kilchoan, Ardnamurchan, Fort William and Ardnamurchan, Highland, Scotland, UK, dellaite occurs
in late-stage, fracture-controlled replacement veins cutting thermally metamorphosed limestone.
Associated minerals include calcite, spurrite,
kilchoanite, foshagite and
tilleyite. The dellaite may have inclusions of
calcite
(MM 34.1.1-16, HOM).
Alteration
dellaite and calcite to
spurrite and H2O
2Ca6(Si2O7)(SiO4)(OH)2 + 3CaCO3 ⇌
3Ca5(SiO4)2(CO3) + 2H2O
Higher temperatures favour the forward reaction
(MM 34.1.1-16).
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